Technical Sheared Rocker Stud Disaster!

I recently ran into this debacle and I decided that it would be best to make a thread separate from my build thread so that it could be more focused and have a relevant title. I really appreciate the advice! Below is the ghastly sight.

I am using some 1956 heads on my later 389. They are non adjustable and have a 3/8" stud that tapers down to 5/16". I was having some issues with them before the stud even broke. I did not have all of the original nuts and had a lot of problems finding replacements. I finally found some that looked like they would work, but just when I was tightening one of them down a stud broke with little warning, leaving me staring at its shattered remains in horror.

I bought some of the screw in studs that don't have a hex. They are 7/16" on the side that goes in the head and 3/8" on the other side. Will these work? Here is the ebay page: https://www.ebay.com/itm/Mr-Gasket-...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

My biggest worry is whether I can tap the holes myself. I would really like to avoid having to take the heads to the machine shop, I also want to do it right. I have access to a vertical mill at a community workshop, so that might be an option if I can't do it by hand.

I was also not quite sure how to get the broken stud out. I think I should be able to get the other ones out with the socket and washer trick, but I am not sure if the broken has enough threads. I have heard of people using heat, but I definitely don't want to FUBAR the heads!

Thanks a million for the help!!!!!!

 

Thread the stud with a 3/8 fine die. Use stacked washers. Once it is out, use a piloted tap so it goes in straight.

 

You could also make a tapping block from a piece of 1” square stock. You will need access to a drill press, or a mill is even better, once you determine the c-c of the studs you need to very carefully center punch the hole locations. One hole is 3/8” and the other is 7/16”.
Start with the bad stud, once it’s out using the 3/8” hole place the block on the adjacent stud, you now have a 7/16” hole to accurately guide the tap.
Pull one stud at a time, tap that hole and repeat.
If you use this method because you are resting the block on a rough casting let it float, you do not want to put a nut on the stud to hold the block down.

 

I have '56-57 studs & nuts. (Heh Heh) Those are super easy to strip and as you have discovered, are best converted to 3/8. Let me know what you need.

 

Also, those '56 heads are very restrictive for a 389 and you could end up with some major compression.

 

You changed the cam? May need long slot rockers.
SPark

 

I have done a few of those, tapping the press-in stud hole on the later heads. All I used was a 1/2" nut held flat to the head with the tap going through the nut as a guide. Use a new tap and go easy till you are a few threads in. Once in a few threads, back out and remove the nut, then thread as you would any other hole. They need to be bottom tapped, so buy two and cut off the starter threads on one tap and use it as a bottoming tap. It's important that they are all straight, but if one is off a little, it's not the end of the world, the engine will never know the difference. I rigged up a bracket to hold the nut while tapping, it was a really thick starter shim cut down in length with a hole drilled to slip over the next stud. Using washer stacked up, I tighten down the shim to hold the nut, the fork at the end of the shim went around the tap. You could also have a shop grind down the end of the tap to 7/16" for a pilot, then it would be self centering, of course you would need three taps then!

Be sure and check where the rocker ball is riding on the stud. The broken stud in your picture shows a wear mark where the rocker arm has hit the stud, close to the head. That is the correct location. Longer push rods or mismatched heads & block puts the rocker balls to high up on the stud which will be hard to keep tight and adjusted. The rocker ball has a 7/16" ID and it should be 100% on the 7/16" portion of the stud, if it is up into the threaded portion, you will have trouble at some point. I suspect thats what you ran into, the stock nut bottoms out on the shoulder of the stud thus making them nonadjustable. If it doesn't bottom out, it will come loose.

You want these or a similar product,
i-24452864-arp-7-16-x-1-2-rocker-stud-kit-arp-290-7201.html
The head should have a 7/16" hole, 7/16" stud with a 3/8" nut on a stock Pontiac head. This requires you to tap out the head to 1/2"-13 thread.
Or, option two as you see in the next posting I put up, heli-coil the existing holes and install BB Chevrolet studs. Cost is probably about the same when all said and done. Be sure to read what I linked.

Joe

 

Read this, machining-pontiac-screw-studs-232219.html

 

You might see if you can borrow a dowel pin puller. Kind of a collect with a slide hammer or something to grab the broken stud and pull it out.

 

That applies to later heads, not what Falcon H has.

 

Thank you!

The seller sold me the the 389 as a short block, so I used the 56 heads that I already had. I agree that they are far from ideal! They are about 70 ccs, so the compression should be around 10:1.

When I threw the engine together, I used the stock 1955 cam that I had lying around. It was the in the best condition out of the ones that I had.

Thank you for the super detailed instructions!

I never would have thought of that! Thank you!

 

Is that the only reason to use the '56 heads, cost savings because you already had them? There could be valvetrain geometry issues when all is said and done. Seems like the intake pattern changes, too.

 

yeah... The early heads do have a different intake bolt pattern, but I fortunately had an early intake to go with them.

 

I just remembered that the rocker arms are lubricated by the studs and realized that the screw in ones don't have any holes in them. Is the only choice going back to original?

 

I thought they were oiled through the push rods.

 

Here is is picture of one of the intact studs:

 

Well then it looks like you need to find studs made for this application. Maybe some Pontiac specialty dealer has screw in studs that are drilled. Your other choice would be to buy studs that are available and have them drilled. Kind of a time consuming operation. Not sure I would want the job.

 

So did I Rich. How is the oil getting to inside the studs? As I knew both the hydraulic and solid lifer cams oiled up the hollow push rods. After pulling one out with a hot 283 I drilled into the casting and tapped 10/32 threaded holes for set screws to hold them and never had a problem. Left in the studs to do it too.
I've got a friend with a set 265 heads and ask him.

 

Thank you for the help!

 

Falcon, I don’t know what your pushrods look like but if they have holes in the tips they will work with your hydraulic lifters. I don’t know why Pontiac engineers thought it was a good idea to oil the rockers through the studs when there was a simpler way than drilling the studs.
Get a set of later Pontiac rockers that are drilled with a hole at the p/r socket and with hyd. lifters, hollow pushrods and the right rockers you can oil the valve train.

 

Early Pontiac's oil the rocker's thru the #2 and #4?cam bearing's and a passage in the block and then the head to the stud's. (strange but it work's) Fordors is correct, later rockers and pushrod's and you can use the screw in stud's, or you can get regular press in stud's for no machine work, with no problem's. You also need to use polyloc's because you won't be able to torque the rocker's.

 

egads, I just saw your post so I revised what I was going to comment on.
You are right about how the oil gets to the heads. Where the valley meets the upper edge of the deck there is a hole drilled in the deck between cylinders 1 & 3 and 6 & 8, you can see those oil galleys cast in the valley.
The early Pontiac heads in question use a 7/16-14 X 3/8-24 stud when converted to screw-in studs so Falcon can use regular Chevrolet rocker nuts and adjust his lifters the same as if he is doing a SBC.

 

Sure looks like the valve springs are stacked pretty tight.

 

I hadn't noticed that before.....They were pretty hard to get on there! My machine shop lost some of the original valves, so these are replacements. I'm pretty sure they were exactly the same, though.

 

Should be easy enough to check, being you have the valve cover off.

 

The cam has .411 lift if it is stock 4 barrel, 2 barrel engines had .324" lift, so spring clearance might not be an issue.